Antibiotics in the Eradication of Avian Respiratory Mycoplasmosis: A Review of the Literature Together with the Results of Laboratory Trials using Chlortetracycline and Demethylchlortetracycline

Abstract

It was shown experimentally that the feeding of the 2 antibiotics, chlortetracycline and demethylchlortetracycline, at the level of 400 g./ton of mash (without potentiation) did not substantially inhibit experimentally-produced respiratory mycoplasmosis in either chickens or turkeys. Small groups of virus- and Mycoplasma gallisepticum-free birds were housed in wire cages in well-ventilated rooms. The drugs were fed at certain stages of infection and for different lengths of time. In treated birds it was noticed that even when clinical signs had regressed or disappeared, M. galliscpticum (Strain A514) could still be detected in the sinus and tracheal exudates or in the turbinates. The haemagglutination-inhibition (HI) antibody titres were generally as high as in the infected but untreated birds or in those still showing clinical signs. In vitro sensitivity tests carried out on Strain A514 both before and after treatment, showed an increase of approximately 20 times in its resistance to either antibiotic. The significance of these findings is discussed in relation to the control of respiratory mycoplasmosis in the field.